Check Engine Light P0401 on a 2000 Ford F-150

Iskandar Blogger 9:52 PM

Code P0401 on a 2000 Ford F-150 indicates a problem with the EGR system, otherwise known as the exhaust gas re-circulation system. The function of the EGR is to re-introduce burnt exhaust gases back into the cylinders, reducing the formation of oxides of nitrogen, which are harmful to the atmosphere. The EGR is vacuum operated. The system consists of the DPFE, or differential pressure feedback EGR, a vacuum regulator, solenoid and the powertrain control module, or PCM.

Instructions

    1

    Locate the DPFE valve on the top rear of the engine. It is a black box roughly the size of a credit card with two different size vacuum hoses attached on the bottom. It will have an electrical connector in the front. The PCM uses this sensor to determine if the engine is idling, cruising or under load. This information is used to determine when and how much the EGR is opened to regulate the cylinder temperatures. The EGR must never be opened at an idle or the engine will run extremely rough or stall. It only opens when the engine rpm is above an idle and more precisely under load. It will not open the EGR when the engine is cold unless under a heavy load. The engine will run rough or stall at an idle and the fuel economy will drop drastically.

    2

    Look at the two hoses of different sizes at the base of the sensor. Make sure they are installed properly. They will stand erect with the sensor removed, so they must be straight up when engaged in the sensor. If they are twisted in any way, they are crossed.

    3

    Disconnect each hose using the flat-head screwdriver to push them down to remove them. Look inside the hoses. Many times they are clogged up with a white powdery substance close to the sensor. Use the screwdriver to break it up. Bend the hose and tap it to remove the residue. Leave the hoses off.

    4

    Plug the hose from the hand vacuum pump on the hose nipple that has REF above it. Probe the wire marked SIG RET on the front of the sensor plug using the voltmeter and wire-piercing probe. Place the black voltmeter lead on a good engine ground. If it isnt marked, simply test the other two wires. One will be a ground, the other will have battery voltage of 12 volts. You need the one with the low voltage.

    5

    Turn the ignition on but do not start the truck. The voltage must be 0.20 to 0.70 volts. Pump the vacuum pump to 7 to 9 inches of vacuum or HG. Now the voltage must be greater than 4 volts.

    6

    Release the vacuum quickly. The voltage must drop below 0.1 volt in less than 3 seconds. If the sensor failed any of these tests and the wiring looks good, the sensor is bad. If the sensor is good, remove the vacuum pump and replace the bottom hoses.

    7

    Test the EGR vacuum solenoid located close to the EGR valve. It has two vacuum hoses and an electrical connector. It must have a vacuum to one hose as long as the engine is running. The PCM will command the EGR vacuum solenoid to allow engine vacuum to the EGR valve after determining when to open the EGR with the help of the DPFE sensor. Pull the two vacuum hoses off the bottom of the solenoid. Be extremely careful when removing these. They are a stinker when they have been off for a long time. It is very easy to break the plastic nipples off the solenoid. Use the flat-head screwdriver and carefully work them off.

    8

    Start the engine and feel for a vacuum at one of the hoses. If no vacuum is present, follow the hose to the intake manifold and look for it to be disconnected or cracked. Replace the hose if it is damaged. Now that it has a vacuum, twist the hose connector slightly and plug the hose with the vacuum in its original position on the solenoid.

    9

    Connect the length of vacuum hose to the remaining nipple and run it up to the windshield wiper arms. Install a vacuum gauge in the vacuum hose and lay it on a wiper arm. The truck must be driven to check the operation of the valve after you check the EGR.

    10

    Pull the hose off the EGR valve. Install the hand-operated vacuum pump to the EGR. Apply vacuum to the EGR a little at a time. The engine must start to run very rough as the EGR is opened. Do not apply more than 9 inches of vacuum to protect the EGR diaphragm. Watch the vacuum pump gauge and see if the vacuum holds. If it holds, the vacuum the diaphragm is good. If the vacuum drops quickly or the engine shows no reaction as the EGR is opened, the EGR valve is bad. Reconnect the vacuum hose to the EGR.

    11

    Test drive the truck and watch the vacuum gauge. You must see vacuum when cruising or under load.